Revealing mistake: During the beginning, as the newspaper headlines roll, the small text in the articles is actually the same text repeating itself over and over again, something like: "an investigation issued."
Continuity mistake: Ken Branagh and Emma Thompson go into a restaurant, where they greet the owner as Ray. Ray then tells them that the place has no drinks licence and no music because Al the piano player is sick. Minutes later Branagh exclaims "What's going on? I can't believe it. No booze, and Ray's sick."
Continuity mistake: In the part where Mike Church visits Gray Baker in the nursing home, he asks Mr. Baker what Roman Strauss said when asked if he really killed his wife. They show a flashback to when this happened and Roman bends over to tell Mr. Baker the answer. In the next shot Roman is standing up again, and then he is shown bending over again.